Optical Crown glass
Glass lenses have become less common in recent years due to the danger of shattering and their relatively high weight compared to CR-39 plastic lenses. They still remain in use for specialised circumstances, for example in extremely high prescriptions (currently, glass lenses can be manufactured up to a refractive index of 1.9) and in certain occupations where the hard surface of glass offers more protection from sparks or shards of material.
Plastic (CR-39)
Plastic lenses are currently the most commonly prescribed lens, due to their relative safety, low cost, ease of production, and outstanding optical quality. The main drawbacks of many types of plastic lenses are the ease by which a lens can be scratched, and the limitations and costs of producing higher index lenses. CR-39 lenses are the exception to the plastics in that they have inherent scratch resistance which is used currently.
Trivex
Trivex is a relative newcomer that possesses the UV blocking properties and shatter resistance of polycarbonate while at the same time offering far superior optical quality (i.e., higher Abbe value) and a slightly lower density. Its lower refractive index of 1.532 vs. polycarbonate's 1.586, however, may result in slightly thicker lenses. Along with polycarbonate and the various high-index plastics, Trivex is a lab favorite for use in rimless frames, due to the ease with which it can be drilled as well as its resistance to cracking around the drill holes. One other advantage that Trivex has over polycarbonate is that it can be easily tinted.
Polycarbonate
Polycarbonate is lighter weight than normal plastic. It blocks UV rays, is shatter resistant and is used in sports glasses and glasses for children and teenagers. Because polycarbonate is soft and will scratch easily, scratch resistant coating is typically applied after shaping and polishing the lens. Along with Trivex and the high-index plastics, polycarbonate is an excellent choice for rimless eyeglasses.
High-index plastics (thiourethanes)
High-index plastics allow for thinner lenses. The lenses may not be lighter, however, due to the increase in density vs. mid- and normal index materials. For people with strong prescriptions these lenses will be highly beneficial. Aside from thinness of the lens, another advantage of high-index plastics is their strength and shatter resistance, although not as shatter resistant as polycarbonate. This makes them another excellent choice for rimless eyeglasses. As raw materials of High-index plastic lenses, thiourethane based materials such as Mitsui Chemicals' MR SERIES are widely used.
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